Polymer composition and method of using same to produce thermostable insulating materials

ABSTRACT

According to the invention, the polymer composition comprises 8 to 20 parts by weight of polyborsiloxane having a molecular weight of 2,000 to 5,000 and including structural units [BOSi] [(CH 3 ) 2  SiO] with a B:Si molar ratio of 1:4 to 5, 40 to 90 parts by weight of polysiloxane rubber, 10 to 60 parts by weight of an organic polymer which may be polyolefins, copolymers of olefins and dienes, halogenated polyolefins, and halogenated copolymers of olefins and dienes, taken separately or in combination with one another, 2 to 10 parts by weight of branched polyorganosiloxane having a molecular weight of 2,000 to 5,000, of the general formula: ##STR1## WHEREIN: R=CH 3 , C 6  H 5 , a=43 to 50 mole %, b=0 to 2 mole %, c=50 to 55 mole %, as well as 10 to 25 parts by weight of silicon dioxide, and 5 to 10 parts by weight of a variable valency metal oxide. 
     The proposed method of producing thermostable insulating materials from said polymer composition comprises molding said polymer composition on a substrate so as to obtain a blank which is then exposed to ionizing radiation until the absorbed radiation dose reaches 6 to 35 megarads. 
     Thus, on the basis of the proposed polymer composition there are produced thermostable insulating materials which at room temperature have an adhesion to organic polymers of 3 to 6 kgf/cm 2  and to metals, 3 to 7 kgf/cm 2 . Such materials are self-adhesive at room temperatures. They also possess satisfactory physico-mechanical and dielectric properties, as well as high thermal, cold and ozone resistance. 
     The proposed method of producing thermostable insulating materials is quite simple technologically.

The present invention relates to polymer compositions and, moreparticularly, to polymer compositions on the basis of polysiloxane andorganic rubbers, as well as to methods of using such compositions toproduce thermostable insulating materials.

Such compositions find extensive application in electrical engineeringas insulating tapes, rubber-impregnated glass fabrics and varnishedfabrics. They are also used as an electrically and thermally insulatingmaterial in the production and repair of electric equipment. Finally,such compositions are used to produce insulating and anticorrosion bandsto protect gas and oil pipelines.

It is only natural that strength requirements are imposed on polymercompositions of this type, as well as an articles manufactured on theirbasis. As regards insulating tapes on the basis of such compositions,they are to possess the following properties:

1. The tape's adhesive coating is to ensure adhesion of overlappinglayers of the tape which is to be maintained over a period of 15 to 25years despite the effects of moisture and elevated temperatures.

2. The adhesive layer is to impart certain dielectric properties to theinsulating tape which must have an electric strength of no less than 3kV/mm and a volume resistivity of no less than 10¹⁰ ohm.cm even afterthe effects of water.

A method of producing thermostable insulating materials on the basis ofpolymer compositions in question largely determines the properties ofarticles manufactured on the basis of such compositions, taking intoaccount the fact that normally, the materials and articles on theirbasis are produced all at the same time.

There are known liquid polymer compositions on the basis of organicpolymers, mainly, on the basis of polyisobutylene with a molecularweight of 3,000 to 8,000. Such compositions may also comprise differentadditives which play the role of fillers and plasticizers. Suchcompositions feature adhesion of different surfaces, as well asautoadhesion, due to which they are fit for the production of insulatingtapes. The tape manufacturing process is as follows: the polymercomposition is applied onto a substrate which is, for example, a film ofpolyethylene or polyvinylchloride. However, such tapes have a lowthermal stability (in the order of 80° C.), while their adhesive layeris thermoplastic and unstable. As a result, the sphere of application ofsuch insulating tapes is rather limited.

There are further known polymer compositions based on low-viscosityrubbers, for example, polysiloxane rubbers and boron-containingpolymers. Such compositions do not possess adhesion and autoadhesionproperties. To impart such properties to a composition, the latterundergoes chemical vulcanization which is carried out as follows. Avulcanizing agent, for example, an organic peroxide, is added to afiller-containing rubber. The composition is then molded on a substratewhich corresponds to the type of article to be manufactured. The blankthus produced is then heat-treated over a short period of time at 200°to 350° C. The end product may be, for example, insulating tape. Beforeuse, the substrate is separated from the rubber tape. The latter isapplied, layer upon layer, on an article being insulated and warmed upfor a long time at 160° to 200° C., which brings about additionalvulcanization, and accounts for monolithic autoadhesion of the tape'slayers. Insulation tapes thus manufactured feature an increased thermalstability (they can withstand long exposures to temperatures around 180°C.) and are sufficiently elastic and durable. However, such tapes arenot adhesive or autoadhesive at room temperature; moreover, theiradhesion to polymers is nil at room temperature. Monolithic adhesion ofa tape's layers can only be effected after prolonged warming-up of thetape. The latter factor considerably reduces the extent of applicationof such tapes, which is determined in this case by the size of anarticle to be insulated and warmed up. Besides, the warming up requiresspecial equipment. Finally, the type of composition under review isdisadvantageous in that the manufacture thereof requires the use ofperoxides and their attendant explosion hazards.

There is known a composition comprising polyborsiloxane having amolecular weight of 2,000 to 5,000 and including structural units [BOSi][(CH₃)₂ SiO] with a B:Si ratio of 1:4 to 5, as well as polysiloxanerubber, an organic polymer, low-molecular polyorganosiloxane, silicondioxide and variable valency metal oxides with the following ratio ofthe components in terms of parts by weight:

polyborsiloxane, 3 to 8;

polysiloxane rubber, 92 to 97;

organic polymer, 0.5 to 1;

low-molecular polyorganosiloxane, 1 to 5;

silicon dioxide, 30 to 35;

variable valency metal oxide, 10 to 30.

The function of the polysiloxane rubber is performed by dimethylsiloxanepolymers comprising [(CH₃)₂ SiO] units and vinylsiloxane polymerscomprising, apart from the above-mentioned units, ##STR2## units. Themolecular weight of such rubbers is between 150,000 and 900,000.

In such a composition, low-molecular polyorganosiloxane is apolysiloxane rubber having a molecular weight of 5,000 to 40,000 andcomprising [(CH₃)₂ SiO] units. The variable valency metal oxides may beFe₂ O₃, Cr₂ O₃, TiO₂ and some others. The organic polymer is used as anadditive in order to raise the stiffness of the composition. The organicpolymer is added in an amount of 1 part by weight. Normally, it ispolytetrafluoroethylene having a molecular weight of 300,000 to 800,000.

The foregoing composition is prepared as follows.

First, polysiloxane rubber and polyborsiloxane (mixture (1) are mixed ina mixer (which may be a roller mixer). Then, silicon dioxide and anorganic polymer (mixture 2) are mixed in a ball mill. The next step ofthe process is carried out in a mixer (roller mixer). During this step,mixture 2 with low-molecular polyorganosiloxane is added, batch afterbatch, to mixture 1. Finally, a variable valency metal oxide isintroduced until a homogeneous mass is obtained.

In the case of the insulating tape manufacture, the composition thusproduced is applied by extrusion or calendering onto a substrate, forexample, a polyethylene film, in the form of a wet band which is exposedto ionizing radiation (γ-radiation of cobalt-60 or high-speedelectrons). Reels of tape are then packed in polyethylene bags andshipped to consumers. Before use, the substrate is peeled off the rubbertape which is wound, layer upon layer, around an article to beinsulated. The article is then kept for 6 to 48 hours at roomtemperature, which ensures monolithic adhesion of the tape's layers dueto the high autoadhesive capacity of the tape at room temperatures.Articles made of such compositions have an increased thermal stability(they can withstand long exposures to temperatures of up to 250° C. andshort exposures to temperature of up to 400° C. in the air), as well ashigh strength (up to 80 kgf/cm²) and elasticity (the elongation amountsto 300 to 800%).

However, the composition under review is disadvantageous in thatthermostable insulating materials (tapes and rubber-impregnated glassfabrics) produced on the basis of said composition do not adhere topolyethylene and other polymers at room temperature, whereas theiradhesion to metals is not sufficiently high (0.5 kgf/cm²) at roomtemperature.

It is an object of the present invention to provide a polymercomposition which would make it possible to produce thermostableinsulating materials featuring sufficiently high adhesion topolyethylene and other polymers at room temperature and high adhesion tometals at this temperature, and having at the same time goodphysico-mechanical and dielectric properties, as well as high thermal,frost, ozone and water resistance.

It is another object of the invention to provide a method of producingsuch materials.

The foregoing and other objects of the present invention are attained byproviding a polymer composition which comprises polyborsiloxane having amolecular weight of 2,000 to 5,000 and including structural units [BOSi][(CH₃)₂ SiO] with a B:Si molar ratio of 1:4 to 5, polysiloxane rubber,an organic polymer, polyorganosiloxane, silicon dioxide and oxides ofvariable valency metals. According to the invention, the organic polymermay be polyolefins, copolymers of olefins and dienes, halogenatedpolyolefins, and halogenated copolymer of olefins and dienes, takenseparately or in combination with one another. The polyorganosiloxane isbranched polyorganosiloxane having a molecular weight of 2,000 to 5,000of the general formula: ##STR3## wherein: R=CH₃, C₆ H₅, a=43 to 50 mole%, b=0 to 2 mole %, c=50 to 55 mole %, with the following part-by-weightratio of the components: polyborsiloxane, 8 to 20;

polysiloxane rubber, 40 to 90;

organic polymer, 10 to 60;

polyorganosiloxane, 2 to 10;

silicon dioxide, 10 to 25;

variable valency metal oxide, 5 to 10.

The selected type of polyborsiloxane imparts the autoadhesion capacityto the composition of this invention and articles produced on the basisof this composition.

An increase in the amount of polyborsiloxane in the composition abovethe maximum level reduces the hydrolytic stability of the composition,which makes subsequent treatment of the composition more difficult. Adecrease in the amount of polyborsiloxane in the composition below theminimum level results in the fact that the composition and materialsmanufactured on the basis thereof do not have sufficiently strongautoadhesion.

The function of the polysiloxane rubbers can be performed, for example,by dimethylsiloxane rubber containing [(CH₃)₂ SiO] units, vinylsiloxanerubber containing ##STR4## units, methylphenylsiloxane rubber containing##STR5## units, and diphenylsiloxane rubber containing [(CH₃)₂ SiO] [(C₆H₅)₂ SiO] units.

The molecular weight of the selected polysiloxane rubbers is between300,000 and 900,000. Polysiloxane rubber of this molecular weightimparts strength, thermal stability and dielectric properties tomaterials manufactured on the basis of the composition in accordancewith the present invention. A decrease in the amount of rubber in thecomposition significantly affects all the above-mentioned properties,while an increase in the rubber content impairs the adhesion andautoadhesion properties.

As stated above, the function of the organic polymer in the proposedcomposition can be performed by polyolefins, copolymers of olefins anddienes, halogenated polyolefins and halogenated copolymers of olefinsand dienes. These components can be used individually or in anycombination with one another. The organic polymers account for thecomposition's adhesive capacity at room temperature with regard topolymers and significantly raise the composition's adhesion to metalswithin the same temperature range.

The selected branched polyorganosiloxanes are characterized by theirhigh viscosity at room temperature and reduced viscosity at atemperature of 70° to 80° C. For example, the viscosity ofpolydimethylphenylsiloxane is much higher at room temperature than thatof low-molecular polydimethylsiloxane having a molecular weight of 5,000to 40,000 and containing [(CH₃)₂ SiO] units, which is used according tothe known method.

As a result, the composition of this invention and materials produced onits basis have a sufficiently high thermal stability; furthermore, thecompatibility of all the composition's components is remarkablypronounced. Without affecting the adhesive properties of thecomposition, branched polyorganosiloxane reduced the composition'sviscosity with a reduction in the temperature, whereby subsequenttreatment of the composition is greatly facilitated.

The viscosity of branched polyorganosiloxane depends on the type ofradical R (CH₃ or C₆ H₅). With R=C₆ H₅, the viscosity of thepolyorganosiloxane is higher than in the case of R=CH₃.

If the polyorganosiloxane contains vinyl units (b≠O) it is more liableto further chemical transformations. Thus the type of branchedpolyorganosiloxane determines the viscosity and reactivity of thecomposition.

In the composition of this invention, silicon dioxide is a componentwhich improves the mechanical properties of the composition. Pyrogenictypes of silicon dioxide can be used, for example, different grades ofaerosil with different specific surfaces. Precipitated silicon dioxidecan also be used. The optimum content of silicon dioxide in thecomposition is 10 to 25 parts by weight.

The oxides of variable valency metals can be, for example, Fe₂ O₃, Cr₂O₃ and TiO₂.

These oxides play the role of thermal stabilizers and are used in anamount of 5 to 10 parts by weight.

In the proposed polymer composition, the polyolefins can be, forexample, polyisobutylene taken in an amount of 20 to 60 parts by weight.In order to facilitate the processing, the molecular weight ofpolyisobutylene is selected within the range of 5,000 to 50,000. If themolecular weight of polyisobutylene is lower than 5,000, the compositionadheres to the equipment employed in the process of its manufacture. Areduction in the polyisobutylene content below the minimum limit impairsthe adhesive properties of materials produced on the basis of thecomposition of this invention. An increase in the polyisobutylenecontent above 60 parts by weight reduces the durability and thermalstability of insulating materials.

The use of polyethylene, preferably, with a molecular weight of 1,500 to3,000 as the organic polymer accounts for sufficiently low viscositylevels of polymer compositions. This is of great importance when usingpolysiloxane rubbers with a molecular weight between 800,000 and900,000. The optimum polyethylene content is 10 to 15 parts by weight,which accounts for sufficiently high adhesive capacity of thecomposition, as well as a desired viscosity, and makes the polymercomposition sufficiently workable. The above-mentioned molecular weightof polyethylene is selected because of the following considerations.First, it is quite difficult to synthetize polyethylene with a molecularweight below 1,500. On the other hand, polyethylene with a molecularweight of above 3,000 is a solid product which has to be ground to arequired fineness in order to be introduced into the composition.

It is recommended that the polyolefin be a copolymer of ethylene andpropylene, preferably, with a molecular weight of 70,000 to 150,000,taken in an amount of 5 to 20 parts by weight and having a propylenecontent of 35 to 40 mole %. This copolymer accounts for an increasedthermal stability of the composition and, accordingly, of materialsproduced on its basis. With the above-mentioned propylene content in thecopolymer, the latter is a relatively soft type of rubber, whichfacilitates its introduction into the composition and improves theworkability of the composition. It is expedient that this copolymer beused in combination with other organic polymers.

It is advisable that the copolymer of olefin and diene be the copolymerof isobutylene and isoprene, preferably, with a molecular weight of3,000 to 60,000, taken in an amount of 20 to 60 parts by weight andhaving an isoprene content of 0.6 to 3 mole %. It can also be thecopolymer of ethylene, propylene and ethylidene norbornane, preferably,with a molecular weight of 70,000 to 150,000, taken in an amount of 5 to20 parts by weight and having a propylene content of 35 to 40 mole % andan ethylidene norbornane content of 1 to 3 mole %.

On the one hand, the foregoing molecular weights and ingredient ratiosof the last three types of polymers account for satisfactory workabilityof the composition. On the other hand, they account for the requiredproperties of the composition, such as adhesion, autoadhesion, thermalstability, etc.

The halogenated polyolefins may be, for example, bromatedpolyisobutylene taken in an amount of 20 to 60 parts by weight andhaving a molecular weight of 5,000 to 50,000, bromated copolymer ofisobutylene and isoprene taken in an amount of 20 to 60 parts by weightand having an isoprene content of 0.6 to 3 mole % (the molecular weightof the latter copolymer is 3,000 to 60,000). The preferable brominecontent for the halogenated polyolefin and halogenated copolymer is 2 to3 percent by weight. These components make the composition fireproof.

The introduction into the polymer composition of N-bromosuccinimide alsomakes thermostable insulating materials produced on the basis of thiscomposition fireproof. N-bromosuccinimide is introduced in an amount of2 to 6 parts by weight. This is an optimum amount at whichN-bromosuccinimide is completely bonded with the organic polymer.

According to the invention, the proposed method for producingthermostable insulating materials is characterized by the polymercomposition of this invention being molded on a substrate, and theresultant blank being exposed to ionizing radiation to reach an absorbedradiation dose of 6 to 35 megarads.

The substrate may be, for example, a film of polyethylene,polyvinylchloride, or polyimide. It may also be paper impregnated, forexample, with wax. Finally, it may be a fabric, such as organosilicon,capron, glass fabric, etc.

The ionizing radiation source may be, for example, radioactive Co₆₀, orhigh-speed electrons.

Organic polymers, such as polyolefins, copolymers of olefins and dienes,and halogenated derivatives of these two types are known to degradepartially or completely after exposure to ionizing radiation. It is alsoknown that polymer compositions on the basis of polysiloxane rubbers andpolyborsiloxanes vulcanize under the action of ionizing radiation. Itcould be expected, therefore, that a composition comprising saidcomponents would degrade when exposed to ionizing radiation. Inactuality, the proposed polymer composition vulcanizes and makes itpossible to manufacture thermostable insulating materials possessing allthe required physico-mechanical properties. This is due to the fact thatan exposure of the proposed composition to ionizing radiation results inthe formation of free radicals from organic polymers (which partiallydegrade) and polysiloxane rubbers which interact with each other,whereby a common vulcanizing network is produced. The latter factorrules out further degradation of the organic polymers.

The co-vulcanization of the borsiloxane and siloxane components accuntsfor autoadhesion of insulating materials; the organic polymers, whichare grafted to siloxane units, account for adhesion of the material topolymers and raise its adhesion to metals.

It is possible to manufacture articles of different configurations fromthermostable insulating materials produced on the basis of the proposedcomposition. The molding conditions are determined by the type ofarticle to be manufactured. In some cases it is advisable that thepolymer composition of this invention be molded at a temperature of 60°to 100° C. and a pressure of 20 to 100 atm; this applies, for example,to the molding of plates of different shapes.

The foregoing temperature and pressure ranges are the optimum. Reducingthe temperature and pressure below the minimum limit would impair thequality of materials (articles) being produced, whereas raising thetemperature and pressure above the maximum level would make the polymercomposition less fabricable (the composition adheres to the equipment).

In general, in order to raise the thermal stability of the material, itis desirable that the polymer composition be molded on a substrate whichhas already been exposed to ionizing radiation so that the absorbedradiation dose amounts from 5 to 50 megarads. This is particularlyadvisable when the substrate is a film of such polymers (polyethylene,polyvinylchloride) which cross-link when exposed to high-energyradiation. For instance, the thermal stability of non-irradiatedpolyethylene is 80° C. When irradiated with γ-rays so that the absorbedradiation dose amounts to 25 megarads, the thermal stability ofpolyethylene reaches 110° C.

The optimum absorbed radiation dose of a blank which is molded on asubstrate is 7 to 12 megarads.

At room temperature, thermostable insulating materials produced on thebasis of the proposed polymer composition possess an adhesive capacityof about 3 to 6 kgf/cm² with regard to organic polymers, and 3 to 7kgf/cm² with regard to metals; these materials are autoadhesive at roomtemperatures.

Such materials possess satisfactory physico-mechanical properties,including a sufficiently high thermal stability (130° to 150° C. atprolonged exposures to elevated temperatures, and 250° C. at shortexposures), cold resistance (-50° C.), and ozone resistance. Theseproperties remain intact after materials have been stored for 7 to 24months at 20° C.

Such materials also possess satisfactory dielectric properties: theirelectric strength is 10 to 25 kV/mm, volume resistivity is 10¹² to 10¹³ohm.cm, and permittivity is 3 to 3.5. These properties are not impairedby moistening.

For example, thermostable insulating tapes produced from such materialshave a frost resistance factor of 0.1 to 1.0 at -50° C. As stated above,such tapes have an electric strength of 10 to 25 kV/mm, permittivity of3 to 3.7, and volume resistivity of 10¹² to 10¹³ ohm.cm. Storage during7 to 24 months does not affect these properties. The adhesive capacityof such tapes is preserved to a large extent (33 percent of the originalvalue) during 1,000 hours after aging at 110° C. Weight losses afteraging during 500 hours at 110° C. do not exceed 5 percent.

Due to the use of organic polymers in the proposed composition,polysiloxane rubber, silicon dioxide and oxides of variable valencymetals are introduced in lesser quantities than in the case of similarcompositions based on polysiloxane rubbers. This accounts for theabove-mentioned combination of properties of thermostable insulatingmaterials, which are superior to those of the known polymercompositions.

Insulating materials produced in accordance with the present inventioncan be used for cable connections and in the production of cable boxesintended for voltages of 1 to 35 kV; such materials are also used foranticorrosion insulation of gas and oil pipelines. For the latterpurpose, such materials can be used in combination with conventionalinsulating materials of similar types.

The basic initial components for the production of the polymercomposition of this invention, i.e. polysiloxane and organic polymers,are readily available.

The process of producing thermostable insulating materials according tothe invention is quite economical and makes it possible to manufacturearticles of different types and configurations.

The proposed method for producing thermostable insulating materials istechnologically simple and carried out as follows.

In order to prepare the composition, its components are mixed with theaid of rubber mixers or roller-type mixers at a temperature of 20° to160° C. Preferably, the sequence of the production steps is like this.First, there is added an organic polymer, for example, polyisobutyleneor a copolymer of isobutylene and isoprene or their halogenatedderivatives, or polyisobutylene with N-bromosuccinimide. Then, to theorganic polymer there are successively added polysiloxane rubber,polyborsiloxane, aerosil with a low-molecular polyorganosiloxane, and avariable valency metal oxide.

If the organic polymer used in the process is liquid, for example, if itis low-molecular polyethylene, polysiloxane rubber is added first,whereafter there are added the organic polymer and polyborsiloxane. Theremaining components are added as indicated above.

If use is made of a mixture of solid and liquid organic polymers, thecomponents are introduced in the following order: the solid organicpolymer, polysiloxane rubber, liquid organic polymer, andpolyborsiloxane, the remaining components being added as indicatedabove.

The result is a rubber mix which is successively passed through arefiner and a strainer in order to eliminate tramps.

The polymer composition thus produced is molded on a substrate, wherebythere is produced a blank which is exposed to ionizing radiation toreach an adsorbed radiation dose of 6 to 35 megarads, preferably, 7 to12 megarads. The polymer composition may be molded at a temperature of60° to 100° C. and a pressure of 20 to 100 atm, for example, in amolding press. The molding conditions are determined by the type ofarticle being manufactured.

In some cases it is preferable that the polymer composition should bemolded on a substrate pre-irradiated to an absorbed radiation dose of 5to 50 megarads.

For example, in order to manufacture insulating tape, the polymercomposition is extruded or calendered onto a non-irradiated orirradiated substrate, for example, a film of polyethylene, in the formof a green band. The blank thus produced is exposed to ionizingradiation. The radiation source may be, for example, γ-radiation ofCo₆₀, or high-speed electrons.

Rolls of finished tape are packed in polyethylene bags and shipped toconsumers. Before use, the substrate is peeled off, so that only therubber tape is used as insulation; the tape can also be used with thesubstrate. In both cases the insulating tape is wound around an articleto be insulated which is kept for 6 to 48 hours at room temperature. Asa result, the tape layers effectively adhere to each other; the tapeitself adheres to the article due to its high adhesion and autoadhesioncapacity at room temperatures.

The objects and advantages of the present invention will be more readilyunderstood from the following examples of preferred embodiments thereof.

EXAMPLE 1

45 parts by weight of methylvinylsiloxane rubber having a molecularweight of 500,000 and a methylvinylsiloxane unit content of 0.07 mole %,5 parts by weight of copolymer of ethylene and propylene with apropylene unit content of 35 mole %, 50 parts by weight ofpolyisobutylene with a molecular weight of 19,000, 12 parts by weight ofpolyborsiloxane with a B:Si molar ratio of 1:5 and a molecular weight of2,000, 5 parts by weight of polydimethylphenylsiloxane with a molecularweight of 2,000, 15 parts by weight of aerosil, and 5 parts by weight ofFe₂ O₃ are mixed in a roller mixer at a temperature of 50° to 60° C. Therubber mix thus obtained is passed through a laboratory refiner with aclearance between the rollers of less than 0.08 mm (this is done at thesame temperature) and then through a strainer in order to separatetramps. The resultant polymer composition is listed in Table 1.

EXAMPLE 2

A polymer composition is prepared as in Example 1, but instead of thecopolymer of ethylene and propylene the composition includes 5 parts byweight of the copolymer of ethylene, propylene and ethylidene norbornanehaving a molecular weight of 80,000, a propylene content of 35 mole %and an ethylidene norobornane content of 1.1 mole %. The resultantcomposition is listed in Table 1.

EXAMPLE 3

A polymer composition is prepared as in Example 1. The compositioncomprises 45 parts by weight of dimethylsiloxane rubber with a molecularweight of 400,000, 5 parts by weight of the copolymer of ethylene andpropylene containing 35 mole percent of propylene units, 50 parts byweight of polyisobutylene with a molecular weight of 19,000, 10 parts byweight of polyborsiloxane with a B:Si molar ratio of 1:4 and a molecularweight of 5,000, 5 parts by weight of polydimethylphenylsiloxane havinga molecular weight of 5,000, 15 parts by weight of aerosil, and 5 partsby weight of Fe₂ O₃. The resultant composition is listed in Table 1.

EXAMPLE 4

A polymer composition is prepared as in Example 1. The compositioncomprises 43 parts by weight of dimethylsiloxane rubber having amolecular weight of 400,000, 7 parts by weight of the copolymer ofethylene and propylene having a molecular weight of 150,000 and apropylene unit content of 35 mole %, 50 parts by weight ofpolyisobutylene having a molecular weight of 19,000, 10 parts by weightof polyborsiloxane with a B:Si molar ratio of 1:4 and a molecular weightof 5,000, 5 parts by weight of polydimethylphenylsiloxane having amolecular weight of 5,000, 15 parts by weight of aerosil, and 5 parts byweight of Fe₂ O₃. The resultant composition is listed in Table 1.

EXAMPLE 5

A polymer composition is prepared as in Example 3, but it contains 40parts by weight of dimethylsiloxane rubber having a molecular weight of450,000 and 10 parts by weight of the copolymer of ethylene andpropylene of Example 4. The resultant composition is listed in Table 1.

EXAMPLE 6

A polymer composition is prepared as in Example 5, but it contains 12parts by weight of polyborsiloxane of Example 4. The resultantcomposition is listed in Table 1.

EXAMPLE 7

A polymer composition is prepared as in Example 1. The compositioncomprises 30 parts by weight of methylvinylsiloxane rubber having amolecular weight of 900,000 and a methylvinylsiloxane unit content of0.07 mole %, 20 parts by weight of the copolymer of ethylene andpropylene having a molecular weight of 70,000 and a propylene content of35 mole %, 50 parts by weight of polyisobutylene having a molecularweight of 50,000, 8 parts by weight of polyborsiloxane with a B:Si molarratio of 1:4 and a molecular weight of 5,000, 5 parts by weight ofpolydimethylmethylsiloxane having a molecular weight of 5,000. 12 partsby weight of aerosil, and 10 parts by weight of Fe₂ O₃. The resultantcomposition is listed in Table 1.

EXAMPLE 8

40 parts by weight of dimethylsiloxane rubber having a molecular weightof 400,000, 10 parts by weight of the copolymer of ethylene, propyleneand ethylidene norbornane having a molecular weight of 70,000 and apropylene content of 40 mole % and an ethylidene norbornane content of 3mole %, 50 parts by weight of polyisobutylene having a molecular weightof 19,000, 9 parts by weight of polyborsiloxane having a B:Si molarratio of 1:4 and a molecular weight of 5,000, 3 parts by weight ofpolydimethylmethylvinylphenylsiloxane having a molecular weight of3,000, a methylvinylsiloxane unit content of 2 mole % and aphenylsiloxane unit content of 43 mole %, 12 parts by weight of aerosil,and 5 parts by weight of Fe₂ O₃ are mixed in a closed Banbury mixerduring 45 minutes at a temperature of 85° to 160° C. The rubber mix istreated as in Example 1. The resultant polymer composition is listed inTable 1.

EXAMPLES 9 through 38

Polymer compositions are prepared as in Example 1. The compositions arelisted in Table 1.

According to Examples 9 through 19, 22, 23 and 31, use is made of thecomponents of Example 1.

According to Example 20, use is made of a mixture of solidpolyisobutylene with a molecular weight of 19,000 and liquidpolyisobutylene having a molecular weight of 8,000, the weight ratiobetween the two being 4:1, respectively.

According to Example 21, use is made of polyisobutylene with a molecularweight of 8,000.

According to Example 24, use is made of methylvinylsiloxane rubberhaving a molecular weight of 500,000 and a methylvinylsiloxane unitcontent of 1 mole %.

According to Example 27, use is made of bromated polyisobutylene with amolecular weight of 25,000 and a bromine content of 3 percent by weight.

According to Example 33, use is made of the copolymer of isobutylene andisoprene having a molecular weight of 3,000 and an isoprene content of0.6 mole %.

According to Example 34, use is made of the copolymer of Example 33,having a molecular weight of 60,000 and an isoprene content of 3 mole %.

According to Example 35, use is made of polyisobutylene having amolecular weight of 19,000, and liquid polyethylene having a molecularweight of 1,500.

According to Example 36,use is made of liquid polyethylene with amolecular weight of 3,000.

According to Example 37, use is made of the bromated copolymer ofisobutylene and isoprene having a molecular weight of 60,000, anisoprene content of 0.6 mole % and a bromine content of 2 percent byweight.

According to Example 38, use is made of the bromated copolymer ofisobutylene and isoprene with a molecular weight of 3,000, an isoprenecontent of 3 mole % and a bromine content of 3 percent by weight.

EXAMPLE 39

The polymer composition of Example 1 is molded in the form of a cord ofa round section with a diameter of 25 mm. This is done by passing thecomposition through an extruder. The cord is then passed through aprofiling calender provided with a winding-up means. At the same timeinto the bite of the calender there is fed polyethylene film having athickness of 60 mu. As a result, there is produced a blank in the formof a band which comprises the polymer composition molded on a substrate(the latter being the polyethylene film). The blank is 0.6 to 0.9 mmthick. The blank is wound up into rolls having a diameter of 10 to 12 cmand a width of 8 to 9 cm, and is vulcanized through an exposure toγ-radiation of Co₆₀. The absorbed dose is 7 megarads. The results oftesting the thermostable insulating tape thus produced are listed inTable 2.

EXAMPLE 40

The polymer composition of Example 2 is molded as in Example 39 on afilm of black-containing polyethylene (the black content amounts to 0.5percent by weight). The film is 0.2 mm thick. The results of testing thetape are tabulated in Table 2.

EXAMPLE 41

The polymer composition of Example 3 is molded as in Example 39 in theform of a cord with a diameter of 7 mm, wherefrom there is produced atape which is 25 mm wide. The blank is vulcanized till an absorbedradiation dose amounts to 8 megarads. The results of testing the tapeare listed in Tables 2 and 3.

EXAMPLES 42 through 68

The polymer compositions of Examples 4 through 30 are molded as inExample 39. According to all these examples, there is molded a cord witha diameter of 14 mm. The width of the insulating tape is 50 mm.

According to Example 43, the substrate is a pre-irradiated polyethylenefilm (the absorbed radiation dose is 5 megarads).

According to Example 45, the substrate is polyvinylchloride filmcontaining TiO₂. The film has a thickness of 0.15 mm.

According to Examples 46, 48, 58, 62 and 66, the substrate ispolyvinylchloride film with a thickness of 0.1 mm.

According to Examples 47, 59, 64, 65 and 68, the substrate is varnishedsilicone fabric having a thickness of 0.15 mm; according to Example 61,the substrate is capron fabric with a thickness of 0.1 mm.

The absorbed radiation doses and the results of testing these tapes(without the substrates) are listed in Table 2. Additional informationwith regard to Examples 42, 46, 50, 51, 56, 57, 62 and 65 is containedin Table 3.

The insulating tape of Example 43 can be used with the substrate. Inthis case the tape's strength amounts to 33 kgf/cm².

EXAMPLE 69

The polymer composition of Example 31 is placed in a press mold havinginner dimensions of 120×120×1 mm, whose bottom and cover are lined withtracing paper. The composition is then press-molded at a pressure of 100atm and a temperature of 80° C. during 15 minutes.

The blank thus obtained is exposed to ionizing radiation. The absorbedradiation dose and the results of testing are listed in Table 2.

EXAMPLES 70 THROUGH 74

The polymer composition of Examples 32 through 36 is molded as inExample 39.

According to Examples 70 and 73, the substrate is varnished siliconefabric having a thickness of 0.15 mm.

According to Example 71, the substrate is polyvinylchloride film with athickness of 0.1 mm. The molded blank is covered with polyethylene filmand exposed to ionizing radiation.

According to Examples 72 and 74, the substrate is polyethylene filmhaving a thickness of 60 mu.

The absorbed radiation doses and the results of testing the tapes thusproduced (without the substrates) are listed in Table 2. Additional datawith regard to testing the tape of Example 74 are listed in Table 3.

The testing data with regard to Example 71 are related to an insulatingtape with a substrate of polyvinylchloride.

EXAMPLES 75 AND 76

The polymer compositions of Examples 37 and 38 are molded as in Example69 at a temperature of 100° C. and a pressure of 20 atm.

The substrate is of tracing paper. The absorbed radiation doses andtesting results are listed in Table 3.

                                      Table 1                                     __________________________________________________________________________    COMPONENTS OF POLYMER COMPOSITION, PARTS BY WEIGHT                            Organic Copolymers                                                                                      Bromated                                                                      copoly-     Copolymer                                                         mer of                                                                              Copolymer                                                                           of ethyl-   Polysiloxane                         Copolymer        isobuty-                                                                            of ethy-                                                                            ene, propy- rubber                               of isoby-                                                                            Poly-                                                                             Bromated                                                                            lene  lene and                                                                            lene, ethy-                                                                         N-bromo-                                                                            Dimethyl-                                                                           Methylvinyl-          Serial                                                                            Polyiso-                                                                           tylene and                                                                           ethy-                                                                             polyiso-                                                                            and iso-                                                                            propy-                                                                              lidene nor-                                                                         succini-                                                                            siloxane                                                                            siloxane              No. butylene                                                                           isoprene                                                                             lene                                                                              butylene                                                                            prene lene  bornane                                                                             mide  rubber                                                                              rubber                1   2    3      4   5     6     7     8     9     10    11                    __________________________________________________________________________    1   50   --     --  --    --     5    --    --    --    45                    2   50   --     --  --    --    --     5    --    --    45                    3   50   --     --  --    --     5    --    --    45    --                    4   50   --     --  --    --     7    --    --    43    --                    5   50   --     --  --    --    10    --    --    40    --                    6   50   --     --  --    --    10    --    --    40    --                    7   50   --     --  --    --    20    --    --    --    30                    8   50   --     --  --    --    --    10    --    40    --                    9   50   --     --  --    --    15    --    --    --    35                    10  50   --     --  --    --    20    --    --    --    30                    11  40   --     --  --    --    10    --    --    --    50                    12  40   --     --  --    --    10    --    --    --    50                    13  40   --     --  --    --    10    --    --    --    50                    14  40   --     --  --    --    10    --    --    --    50                    15  30   --     --  --    --    20    --    --    --    50                    16  50   --     --  --    --    --    --    --    --    50                    17  50   --     --  --    --    --    --    --    --    50                    18  50   --     --  --    --    --    --    --    --    50                    19  50   --     --  --    --    --    --    --    --    50                    20  50   --     --  --    --    --    --    --    --    50                    21  50   --     --  --    --    --    --    --    --    50                    22  50   --     --  --    --    --    --    --    --    50                    23  50   --     --  --    --    --    --    --    --    50                    24  50   --     --  --    --    --    --    6     --    50                    25  50   --     --  --    --    --    --    2     --    50                    26  50   --     --  --    --    --    --    --    --    50                    27  --   --     --  50    --    --    --    --    --    50                    28  60   --     --  --    --    --    --    --    --    40                    29  60   --     10  --    --    --    --    --    --    40                    30  45   --     15  --    --    --    --    --    --    40                    31  40   --     --  --    --    --    --    --    --    50                    32  40   --     10  --    --    --    --    --    --    50                    33  --   40     10  --    --    --    --    --    --    50                    34  --   40     --  --    --    --    --    --    --    60                    35  20   --     10  --    --    --    --    --    --    80                    36  --   --     10  --    --    --    --    --    --    90                    37  --   --     --  --    50    --    --    --    --    50                    38  --   --     10  --    40    --    --    --    --    50                    __________________________________________________________________________                       Branched polyorganosiloxane                                                                   Polydimethyl-                                                                             Precipi-                                     Polybor-                                                                           Polydimethyl-                                                                         Polydimethyl-                                                                         methylvinyl-                                                                              tated                                    Serial                                                                            siloxane                                                                           phenylsiloxane                                                                        methylsiloxane                                                                        phenylsiloxane                                                                        Aerosil                                                                           SiO.sub.2                                                                          Fe.sub.2 O.sub.3                                                                  TiO.sub.2                                                                        Cr.sub.2                                                                      O.sub.3                      No. 12   13      14      15      16  17   18  19 20                 __________________________________________________________________________              1   12   5       --      --      15  --   5   -- --                           2   12   5       --      --      15  --   5   -- --                           3   10   5       --      --      15  --   5   -- --                           4   10   5       --      --      15  --   5   -- --                           5   10   5       --      --      15  --   5   -- --                           6   12   5       --      --      15  --   5   -- --                           7    8   --      5       --      12  --   10  -- --                           8    9   --      --      3       12  --   5   -- --                           9   14   5       --      --      15  --   10  -- --                           10  12   2       --      --      12  --   10  -- --                           11  12   5       --      --      15  --   10  -- --                           12   9   5       --      --      15  --   5   -- --                           13   9   5       --      --      15  --   5   3  --                           14  10   5       --      --      15  --   10  -- --                           15  10   5       --      --      15  --   5   -- --                           16  12   5       --      --      15  --   10  -- --                           17  12   5       --      --      15  --   5   -- --                           18  10    10     --      --      15  --   5   -- --                           19  10   5       --      --      15  --   5   -- --                           20  10   5       --      --      15  --   5   -- --                           21  10   5       --      --      15  --   5   -- --                           22  9    5       --      --      15  --   5   3  --                           23  8    5       --      --      15  --   5   -- --                           24  8    1       --      --      18  --   5   -- --                           25  8    1       --      --      18  --   5   -- --                           26  8    5       --      --      --  15   5   -- --                           27  8    5       --      --      5   7,5  5   -- --                           28  8    5       --      --      18  --   10  -- --                           29  8    2       --      --      18  --   10  -- --                           30  8    1       --      --      10  --   10  -- --                           31  8    2       --      --      10  --   5   -- --                           32  8    3       --      --      10  --   10  -- --                           33  20   3       --      --      10  --   10  -- --                           34  20   3       --      --      15  --   5   -- --                           35  8    5       --      --      --  20   10  -- --                           36  8    5       --      --      25  --   10  -- --                           37  8    2       --      --      10  --   10  -- --                           38  8    1       --      --      10  --   --  -- 5                  __________________________________________________________________________

                                      Table 2                                     __________________________________________________________________________             Physico-Mechanical Characteristics                                   Radiation         After Ageing during                                                                     Adhesion, kgf/cm.sup.2                                                                  Equilibrium Swelling,                   Serial                                                                            dose,                                                                              Initial at 20° C.                                                               48 hours at 150° C.                                                              to poly-                                                                            to  wt. %                                   No  megarads                                                                           P L   L  P L   L   ethylene                                                                            steel                                                                             gasoline                                                                            water                             1   2    3 4   5  6 7   8   9     10  11    12                                __________________________________________________________________________    39  7    11                                                                              850 44 28                                                                              405 53  4.1   7.1 249   1.6                               40  7    14                                                                              845 64 20                                                                              360 28  3.8   5.9 244   2.2                               41  8    12                                                                              980 64 14                                                                              520 76  5.7   6.9 291   1.3                               42  8    15                                                                              970 58 14                                                                              470 68  4.0   5.0 327   2.2                               43  6    14                                                                              1030                                                                              76 14                                                                              455 48  4.6   6.0 230   1.1                               44  7.5   7                                                                              1170                                                                              84 14                                                                              350 60  5.7   7.0                                         45  8     6                                                                              1020                                                                              220                                                                               8                                                                              275 15  5.1   6.0                                         46  8.9  10                                                                              960 66  8                                                                              670 70  4.4   5.5                                         47  7    12                                                                              1160                                                                              108                                                                               9                                                                              450 66                                                    48  7     5                                                                              1070                                                                              96  4                                                                              500 32  4.5   5.8                                         49  7    19                                                                              930 57 15                                                                              740 16  4.8   6.8                                         50  7.2  17                                                                              840 52 14                                                                              600 52  3.6   5.4       1.3                               51  7.2  15                                                                              780 47 11                                                                              580 70  3.6   5.0       2.6                               52  8.3  12                                                                              1100                                                                              52 13                                                                              720 56  4.1   5.4                                         53  8.3  14                                                                              810 56 12                                                                              680 26  4.2   5.5                                         54  8    19                                                                              825 26 15                                                                              570 44  4.7   5.9                                         55  8    16                                                                              780 46 24                                                                              500 12  5.2   5.9                                         56  8.3  16                                                                              1000                                                                              62 17                                                                              575 40  4.2   6.2 294   2.6                               57  8    16                                                                              845 51 20                                                                              575 55  3.8   5.6                                         58  7    13                                                                              940 46 20                                                                              285 11  4.2                                               59  10.1 10                                                                              1240                                                                              60 23                                                                              690 40  4.6                                               60  7.2  17                                                                              790 40 15                                                                              3,390                                                                             48  4.0   6.2       2.2                               61  8    15                                                                              750 30 22                                                                              260 14  3.4   5.1       2.4                               62  9.8  16                                                                              755 28           4.0   5.1                                         63  7.3  11                                                                              1560                                                                              64           3.9   5.2                                         64  8     7                                                                              760 24 22                                                                              565 28  4.0                                               65  7.4  13                                                                              945 32 20                                                                              355 18  3.6                                               66  3.5   6                                                                              680 68  6                                                                              210 66  5.5   6.1                                         67  8.5   7                                                                              1230                                                                              96  5                                                                              350 100 3.8   5.2                                         68  10.2 15                                                                              1120                                                                              40           3.5                                               69  11.2  9                                                                              690 12           2.4                                               70  12    8                                                                              855 12           3.1                                               71  7    50                                                                              200  5           3.6                                               72  9     9                                                                              1560                                                                              106                                                                               5                                                                              630 60  2.7   3.7                                         73  11.7 11                                                                              355  4 14                                                                              310 13  1.5                                               74  9    33                                                                              505 29 27                                                                              330 14  0.9       378                                     75  12.5 17                                                                              730 17           2.3                                               76  12.5 10                                                                              530  8           3.1       204                                     __________________________________________________________________________     P is tensile strength, kgf/cm.sup.2                                           L is yield strength, %                                                        l is permanent elongation, %                                             

                                      Table 3                                     __________________________________________________________________________    Physical-Mechanical Characteristics After Ageing                                  120° C.                                                                       150° C.                                                                       180° C.                                                                       200° C.                                                                       250° C.                                Serial                                                                            120 days                                                                             15-20 days                                                                           2 days 1 day  1 hour  Adhesion, kgf/cm.sup.2                No  P L  l P L  l P L  l P L  l P  L  l to copper                                                                          to aluminum                      __________________________________________________________________________    41         19                                                                              185                                                                              36       29                                                                               95                                                                              18        7.0  7.2                              42         20                                                                              130                                                                              26                                                                              38                                                                               95                                                                              12                                                                              23                                                                               79                                                                              12                                                                              28  75                                                                              10                                      46         14                                                                              235                                                                              32                                                                              23                                                                              220                                                                              30                                                                              12                                                                              330                                                                              82                                                                              6  245                                                                              47                                                                              6.6  7.0                              47         25                                                                              250                                                                              24                                                                              27                                                                              220                                                                              32                                                                              38                                                                              145                                                                              20                                                                              8  105                                                                              19                                      48         13                                                                               65                                                                              13              5  260                                                                              88                                      50  25                                                                              150                                                                              6 27                                                                              235                                                                              20       27                                                                              140                                                                              22                                                                              6   70                                                                              38                                      51  24                                                                              145                                                                              6 32                                                                              190                                                                               8                                                                              15                                                                              310                                                                              44                                                                              21                                                                              225                                                                              70                                                                              5  460                                                                              66                                                                              6.5  6.7                              56                              4  210                                                                              52                                                                              6.3                                   57                       16                                                                              110                                                                              14                                                                              5   70                                                                              18                                      62         40                                                                               50                                                                               2       13                                                                              120                                                                              22                                              65  25                                                                              110                                                                              7 35                                                                               90                                                                               4       16                                                                              165                                                                               6                                              74                       27                                                                              240                                                                               4                                              __________________________________________________________________________     P, L and l are as in Table 2.                                            

What is claimed is:
 1. A polymer composition comprising 8 to 20 parts byweight of polyborsiloxane having a molecular weight of 2,000 to 5,000and containing structural units [BoSi] [(CH₃)₂ SiO] with a B:Si molarratio of 1:4 to 5, 40 to 90 parts by weight of polysiloxane rubber, 10to 60 parts by weight of an organic polymer selected from the groupconsisting of polyolefine, copolymers of olefins and dienes, halogenatedpolyolefins and halogenated copolymers of olefins and dienes, 2 to 10parts by weight of branched polyorganosiloxane having a molecular weightof 2,000 to 5,000 of the general formula: ##STR6## wherein: R is aradical selected from the group of radicals composed of CH₃, C₆ H₅ ;a=43 to 50 mole %, b=0 to 2 mole %, c=50 to 55 mole %, 10 to 25 parts byweight of silicon dioxide, and 5 to 10 parts by weight of a variablevalency metal oxide.
 2. A polymer composition as claimed in claim 1,wherein the polyolefin is polyisobutylene taken in an amount of 20 to 60parts by weight.
 3. A polymer composition as claimed in claim 1, whereinthe polyolefin is polyethylene taken in an amount of 10 to 15 parts byweight.
 4. A polymer composition as claimed in claim 1, wherein thepolyolefin is a copolymer of ethylene and propylene having a propylenecontent of 35 to 40 mole % and taken in an amount of 5 to 20 parts byweight.
 5. A polymer composition as claimed in claim 1, wherein thecopolymer of olefin and diene is a copolymer of isobutylene and isoprenecontaining 0.6 to 3 mole % of isoprene and taken in an amount of 20 to60 parts by weight.
 6. A polymer composition as claimed in claim 1,wherein the copolymer of olefin and diene is a copolymer of ethylene,propylene and ethylidene norbornane taken in an amount of 5 to 20 partsby weight and having a propylene content of 35 to 40 mole % andethylidene norbornane content of 1 to 3 mole %.
 7. A polymer compositionas claimed in claim 1, wherein the halogenated polyolefin is bromatedpolyisobutylene taken in an amount of 20 to 60 parts by weight.
 8. Apolymer composition as claimed in claim 1, wherein the halogenatedcopolymer of olefin and diene is a bromated copolymer of isobutylene andisoprene taken in an amount of 20 to 60 parts by weight and having anisoprene content of 0.6 to 3 mole %.
 9. A polymer composition as claimedin claim 1, which includes N-bromosuccinimide in an amount of 2 to 6parts by weight.